One of the following is not a good way to prevent virus.

Protecting a computer from viruses requires deliberate security practices; the question asks which listed action is not one of these good practices, meaning it is actually a risky behaviour rather than a protective measure.

Carelessly exposing your vital and personal information is not a virus-prevention practice at all. It is a risky behaviour that makes a user more vulnerable, since attackers can use exposed personal details or careless sharing of files and links as a way to trick a user into installing malware or falling for phishing attempts that carry viruses.

The remaining three options are all recognised, active virus-prevention measures. Encryption protects the confidentiality of data so that even if it is intercepted, it cannot be easily read or misused. Using a firewall filters incoming and outgoing network traffic to block unauthorised or malicious connections before they reach the computer. Using antivirus software actively scans for, detects, and removes known viruses and malicious programs.

When a question asks which option is "not" a protective measure, look for the option describing a careless or risky user action, since good security practices are always about actively defending the system, never about exposing it.